correct crank length

It depends what you are riding and why.
There are different lengths. Longer cranks allow you to use more power in each stroke, while shorter cranks make each stoke easier and allow you to 'spin' more easily.
Track bikes use shorter cranks to aviod the crank hitting the raised bank at low speed.
They are measured from the middle of the pedal to the middel of the BB, and are usually 170 or 175mm.

I hope that helps.

Brian

Quoted post said:

Originally posted by ians
Hi

Could someone please tell me how to calculate the correct crank length?

Thanks

Ian

Ian, unfortunatelly I do not know how to calculate the right crank lenght, but I can share my experience with you hoping this would help you decide if you need to change your current length. I had a 175 mm in my original crank arm when I bought my bike, then in order to gain some power I decided to go big with the enormuos 180 mm from Shimano Dura-Ace. After three or four months of using it I realized that I have not really make a significant improvement in speed or power but instead a sudden and rare pain started to build up in my butt and hamstring of my right leg. I am not really sure as the increase in cranck arm lenght contributed or started up my pain. At the end my advice is: consider that if you increase the arm length you are also increasing the diameter of your spinning and all the muscles in your legs will work much harder in a different way, but if you decide to go larger anyway give it at least 1 month to pedal really easy and don't go more than 30 Mi a day. Whatever you do, don't stop riding!.

Thanks guys. I find this whole thing very confusing. I'm a recreational/touring rider. I read somewhere that crank length is a function of inside leg measurement, and if it's not right can cause knee problems.

I've just done a search in Google for 'crank length' and the the first 3 hits give me results varying from 165mm to 175mm.

I guess it's toss a coin time.

Ian

Pete Biggs said:

There are various formulae to work it out but they tend to give different results - some of them
very stupid! I think it's best to use personal experience, preference, intuition and common sense
instead.

170mm is generally considered suitable for average inside leg (average British adult) for normal
road cycling. New MTB's tend to come with
175mm.

Perhaps because the average British adult has been gaining two inches in height per generation, of
late, and the MTB standard has been developed more recently than the road bike? Or just because MTB
frames are designed with higher bottom brackets, so early MTB riders could put longer cranks on
without trouble?

Does *anybody* sell bicycles with 185-190mm cranks off the shelf?

Biktor said:

Ian, unfortunatelly I do not know how to calculate the right crank lenght, but I can share my
experience with you hoping this would help you decide if you need to change your current length. I
had a 175 mm in my original crank arm when I bought my bike, then in order to gain some power I
decided to go big with the enormuos 180 mm from Shimano Dura-Ace. After three or four months of
using it I realized that I have not really make a significant improvement in speed or power but
instead a sudden and rare pain started to build up in my butt and hamstring of my right leg.

Just out of interest, Biktor, how tall are you? How long are your legs?

Quoted post said:

Originally posted by ians
Hi

Could someone please tell me how to calculate the correct crank length?

Thanks

Ian

I have read somewhere that the most efficient length in terms of biomechanic is 41% of tibial length, but when all said and done, there is very little difference between a 165 and a 180mm crank.

Quoted post said:

Originally posted by ians
Hi

Could someone please tell me how to calculate the correct crank length?

Thanks

Ian

An good reference on the subject is Road Racing: Technique and Training by Bernard Hinault. He devotes 4 pages to crank length. The book is a bit dated, but his discussion of the bike and your position on it is very good.

Henry Braun said:

Perhaps because the average British adult has been gaining two inches in height per generation, of
late, and the MTB standard has been developed more recently than the road bike? Or just because
MTB frames are designed with higher bottom brackets, so early MTB riders could put longer cranks
on without trouble?

Does *anybody* sell bicycles with 185-190mm cranks off the shelf?

I don't think anyone even _makes_ 190mm cranks as standard production (a few people may make them
to order).

After rowing for a few years, I started cycling more seriously and soon changed to 185mm cranks. It
felt silly on the 170mm standard twiddling along with my feet spinning away and my thighs hardly
moving. It's hard to see how 185mm can be 'long enough' by any reasonable measure but they are the
longest that are reasonably easy to get hold of.

James

In message <[email hidden]>, ians <[email hidden]> writes

Quoted message said:

Hi

Could someone please tell me how to calculate the correct crank length?

Thanks

Ian

--

Quoted message said:

--------------------------<

Posted via cyclingforums.com cyclingforums.comcyclingforums.comOpen ↗

Lance Armstrong says (The Lance Armstrong Performance Programme):

Inside Leg=crank length
<72cm (28.5 inch) = 165mm 72-80cm (28.5 - 31.5 inch) = 170mm 80-85cm (31.5 - 33.5 inch) = 172.5mm

Quoted message said:

85cm (33.5 inch) = 175mm

Lance is, of course, a high cadence rider which might explain crank lengths that are shorter than
many people would recognise.
--
Michael MacClancy

Is the Inside Leg measurement the measurement from the top of the pedal to the top of the saddle, measuring along the axis of the seat tube?

The measurement from the top of the pedal to the top of the saddle on my bicycles are set to 34.25 inches.

I am 6'2" and 20 years ago, I was set up with a bicycle having crank arm length of 172.5. This bicycle is a 24 inch or 61cm frame from center of BB to top of seat tube. I have a newer bicycle with 175 crank arms. I seem to be able to climb better with the 175 crank arms, but I am faster overall with the bicycle with the 172.5 crank arms. Of course it could be other differences in the bicycles.

What are other riders of my size using?

Dorwinion said:

Is the Inside Leg measurement the measurement from the top of the pedal to the top of the saddle,
measuring along the axis of the seat tube?

The measurement from the top of the pedal to the top of the saddle on my bicycles are set to
34.25 inches.

I am 6'2" and 20 years ago, I was set up with a bicycle having crank arm

I'm trying to picture your bike, and failing. I'm also about 6'2", and I'm rather longer in the back
than average. My road bike frame is 650mm or 25.5". The distance from the centre of the bottom
bracket to the top of by saddle (parallel with the seat tube) is 780mm or 30.75 inches; the distance
from the top of the lower pedal with the crank aligned with the seat tube to the top of the seat
(parallel with the seat tube) is 940mm or 37".

Quoted message said:

length of 172.5. This bicycle is a 24 inch or 61cm frame from center of BB to top of seat tube. I
have a newer bicycle with 175 crank arms. I seem to be able to climb better with the 175 crank
arms, but I am faster overall with the bicycle with the 172.5 crank arms. Of course it could be
other differences in the bicycles.

FWIW the cranks on my hill bike appear to be 175mm centre to centre, and those on my road bike
appear to be 170mm centre to centre. I can't say I notice this difference in practice.

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

There are no messages. The above is just a random stream of bytes. Any opinion or meaning
you find in it is your own creation.

Dorwinion <[email hidden]>typed

Quoted message said:

Is the Inside Leg measurement the measurement from the top of the pedal to the top of the saddle,
measuring along the axis of the seat tube?

No, it's the measurement from *your* crotch bone (pubis) to the floor (without high heels,
shoes etc!).

Quoted message said:

The measurement from the top of the pedal to the top of the saddle on my bicycles are set to
34.25 inches.

That sounds a little low for someone of your height. It's about right for me - 5'6", 31" from pubis
to floor. Your feet add some effective leg length too, don't forget.

Quoted message said:

I am 6'2" and 20 years ago, I was set up with a bicycle having crank arm length of 172.5. This
bicycle is a 24 inch or 61cm frame from center of BB to top of seat tube. I have a newer bicycle
with 175 crank arms. I seem to be able to climb better with the 175 crank arms, but I am faster
overall with the bicycle with the 172.5 crank arms. Of course it could be other differences in the
bicycles.

Quoted message said:

What are other riders of my size using?

Something similar, what ever they can get, probably! Shin, thigh and foot lengths all vary and
affect how some sizes fit different people better.

--
Helen D. Vecht: [email hidden] Edgware.

Quoted message said:

I seem to be able to climb better with the 175 crank arms, but I am faster overall with the
bicycle with the 172.5 crank arms. >

You (obviously) have a bit more leverage with longer cranks, so easier to
climb.But you have to move your legs in bigger circles also, maybe a disadvantage at any sort of
speed. Mind you, I'm no expert, and only 67.8" tall. (Important that 0.8"!).

Niv.

Quoted post said:

Originally posted by Henry Braun

BOn Thu said:

Ian, unfortunatelly I do not know how to calculate the right crank lenght, but I can share my
experience with you hoping this would help you decide if you need to change your current length. I
had a 175 mm in my original crank arm when I bought my bike, then in order to gain some power I
decided to go big with the enormuos 180 mm from Shimano Dura-Ace. After three or four months of
using it I realized that I have not really make a significant improvement in speed or power but
instead a sudden and rare pain started to build up in my butt and hamstring of my right leg.

Just out of interest, Biktor, how tall are you? How long are your legs? [/B]

Henry, I'm 5'11" tall and my legs are about 32-1/2" long.

Quoted post said:

Originally posted by Niv
> I seem to be able to climb better with the 175 crank arms, but I am faster overall with the

Quoted message said:

bicycle with the 172.5 crank arms. >

You (obviously) have a bit more leverage with longer cranks, so easier to
climb.

isn't pedaling force something that you address with your gears though. Crank length is to do with the optimal alignment/movement of the leg joints surely?

best wishes
james

I feel embarrassed! I wrote down the distance from lower pedal (in parallel to the seat tube) to top of saddle from memory, guess I need more Omega 3 or Ginkgo Biloba capsules. The correct distance is 38.25 inches. 😄

pig pog <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

isn't pedaling force something that you address with your gears though. Crank length is to do with
the optimal alignment/movement of the leg joints surely?

Yes and yes. But remember that crank length is actually part of the gearing. As previously
mentioned, changing the crank length does not alter the distance travelled per crank rotation.
However, it does affect the effort required and the distance travelled by the foot. It therefore
follows that a longer crank equates to a lower gear. Conventional gear tables do not take crank
length into account. Canny juniors can exploit this in gear-limited races by using shorter cranks.
This is not really a good idea as the gear limit is supposed to be there for their protection.

Sheldon Brown has a discussion of this on his website, and also a proposed alternative system for
measuring gear size that takes crank length into account. Governing bodies should switch to the
Sheldon method when setting gear limits.

--
Dave...